Generally, a cloud storage service combines physically separated storages into a logical single storage and allocates the storage space on a user basis so that a mass virtual storage can be used by users. Persons, enterprises or organizations join a cloud storage service and are allocated with virtual storage spaces. The amount of the allocated storage space may be different depending on fees for the cloud storage service.
Such cloud storage service is suitable for reduction of storage construction costs, but may have a lot of disadvantages. For example, when small enterprises that do not have a dedicated computer room in terms of cost reduction depend on the cloud storage service, it may not be possible to use data stored in the cloud storage during network interruption.
Meanwhile, a small enterprise having a considerable amount of data constructs a SMB network system that shares data in the enterprise by installing a dedicated NAS in the enterprise and connecting the NAS to computers in the enterprise through a network. In that case, a member of the enterprise in an outside environment (e.g., from outside the enterprise's network) needs to use an extra web folder service to access data stored in the NAS of the SMB. Further, to store data in the NAS, the member of the enterprise in the outside environment should send an e-mail with the file to be stored attached to the email. Moreover, most of the SMB enterprises have only one or two NASs, and a data loss may occur due to disaster and error of the NASs.